The spines of echidnas are just really thick hairs. They’re made out of keratin, which is the same as what our hair and fingernails are made of.

Echidnas’ hind feet point backwards. This is to help them dig better.

Echidnas have a lower body temperature than other mammals, resting at around 30 °C. Their body temperature can also fluctuate 6-8 °C during the day.

You can’t tell if an echidna is male or female by simply looking at them as they have no gender-specific features and their reproductive organs are internal.​

All echidnas are born with spurs on their hind limbs, similar to what male platypuses have. They are not venomous like in platypus, but the glands underneath the spurs secrete pheromones used for attracting each other during breeding season. Females are meant to lose the spurs as they mature but some retain the spurs, while some males lose them.